The case for active crossovers and bi-amping

[JonFo]

Some of us regularly advocate the use of active crossovers and bi-amping for true state of the art results with our great speakers.

And in this recent interview with Roger Sanders, he clearly explains the why's:

"Passive crossovers have dreadful performance. This is another extensive topic that I cannot address adequately in this interview. So just allow me to summarize by saying that passive crossovers have the well-known problems of phase shift, hysteresis losses, group delay, inadequately steep crossover slopes, and distortion. Less appreciated is the fact that they insert inductors, capacitors, and resistors between the amplifier and the speaker's drivers. This isolates the woofer from the amplifier and prevents the amplifier from having tight control of the driver. Or to put it another way, the damping factor of the amplifier is degraded by passive crossovers.

Since it is essential to use the amplifier to control the woofer, the amplifier must be connected directly to its driver without any intervening crossover components. Therefore electronic/active crossovers are essential to obtaining good integration. The amplifier must have a high damping factor. This excludes the use of tube amplifiers for driving woofers because their output impedance is too high. Powerful, well-designed solid state amplifiers have incredibly low output impedance (typically less than 0.1 Ohm), and massive current flow capacity, so they have the high damping factor and power needed to really control a woofer.

It is necessary to use electronic/active crossovers to achieve the best from any speaker system. I continue to be amazed by all the speakers on the market with passive crossovers that claim to be "reference" quality or SOTA systems. The truth is that electronic/active crossovers and multiamplifier systems are superior to any passive crossover system. All speakers will be improved with the proper use of electronic/active crossovers. So any speaker that uses passive crossovers simply cannot be considered the finest available. I am unwilling to compromise and so do not use passive crossovers in any of my current speakers.

There are many diverse types of electronic/active crossovers with many different features. Also, both analog and digital electronic crossovers now are available. I consider digital crossovers to be one of the greatest advances in modern audio. They offer features that I have wanted crossovers to have for years, but which were unavailable. "

From this article: http://www.dagogo.com/View-Article.asp?hArticle=991

Very much worth the read if you care about ESL and good amplification.

So what do you do for bi-amping?

 

[JonFo]

So, no one else bi-amps or does external crossovers?


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[jmschnur]

With the modern Martin Logan speakers how does one do this? I assume ML has designed them to have active xovers between the panel and the amp driving the sub woofer of the hybrid ( summit x, Montis, Ethos, etc)

For the stage center how could this be done.?

Joel

 

[churchill]

I run a electronic/active crossover (Pass XVR-1) with my CLS IIz's and a single JL F112 sub. I cross my panels over to my sub at 88Hz using a 24 db roll. The Pass allows 6 db, 12 db, 18 db and 24 db slopes at various frequencies. I run Pass mono's for amps.

The crossover has really allowed me to dial in my sound and help mate the CLS IIz's with the F112 sub. I've made small adjustments with phase on my sub as well.

 

[|Tch0rT|]

I used to do an all active setup back in my car audio days. I've been dreaming of building an active ESL setup since I got my ML's but I think that's quite a bit down the road.

 

[JonFo]

With the modern Martin Logan speakers how does one do this? I assume ML has designed them to have active xovers between the panel and the amp driving the sub woofer of the hybrid ( summit x, Montis, Ethos, etc)

Yes, the amplified hybrids such as the Ethos use an electronic xover for the bass component, but still use a passive crossover for the high-pass on the panel. It is actually the passive high-pass which robs users of much of the clarity these speakers are actually capable of.

Unlike the Monoliths, none of the modern units have replaceable crossovers. They require opening the unit up and modifying them for active duty.
I've done that to SL3 and Sequels, and it's not a big deal if you are familiar with electronics (no need to be an EE, but some hobbyist experience helps).

For the stage center how could this be done.?

Joel

Again, opening up the unit and performing some mods would allow this. Although due to their design, this is trickier as it requires a three-way crossover (woofer - panel - tweeter), and is more work to measure and adjust the active unit.

Reminder: anyone running their own crossovers needs to own and know how to use an audio measurement system. You have to adjust the delays, crossover points, gains and (optionally) EQ to get as good a match between speaker elements as possible. This takes hours and hours of tedious measurements and adjustments.
The results make it all worthwhile though.

 

[JonFo]

I run a electronic/active crossover (Pass XVR-1) with my CLS IIz's and a single JL F112 sub. I cross my panels over to my sub at 88Hz using a 24 db roll. The Pass allows 6 db, 12 db, 18 db and 24 db slopes at various frequencies. I run Pass mono's for amps.

The crossover has really allowed me to dial in my sound and help mate the CLS IIz's with the F112 sub. I've made small adjustments with phase on my sub as well.

Cool, the CLS + Sub is a great candidate for a good active crossover setup, and your gear is definitely first-class. Adjusting the phase match is indeed critical for ultimate results. A steep xover (like your 24dB) helps that CLS sing in the critical mid-bass without the intrusions from lower frequencies.

 

[JonFo]

I used to do an all active setup back in my car audio days. I've been dreaming of building an active ESL setup since I got my ML's but I think that's quite a bit down the road.

Keep that dream alive, one day it would be fun to hear your 'active' story. It really does make a significant difference.

 

[eknuds01]

So, no one else bi-amps or does external crossovers?


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Jon -

I would like, at some point, to passively bi-amp at first since that does involve opening my speakers up and disabling the external circuitry.

I have no knowledge on how this is done, nor do I know how to connect an external (electronic) crossover and configure it properly. I do not think it's as simple as connecting wire A to wire B and calling it a day.

Erik

 

[JonFo]

Jon -

I would like, at some point, to passively bi-amp at first since that does involve opening my speakers up and disabling the external circuitry.

I have no knowledge on how this is done, nor do I know how to connect an external (electronic) crossover and configure it properly. I do not think it's as simple as connecting wire A to wire B and calling it a day.

Erik

Erik, a passive bi-amp is pretty easy on most ML's as they have historically had distinct high-pass/low-pass section, which wen not biamping, they use post jumpers or let you bi-wire.

If you have one of those models, just remove the jumpers, then run one amp to the panel posts and one amp to the bass posts.

No external crossovers needed in that scenario. Not as high performance, but a step up over just one amp in many cases.

 

[eknuds01]

Jon -

Yes I have the Aerius i, so a passive bi-amp scheme is an option. I'd imagine it will be s ice step up and if I am feeling like taking on another challenge, I can always try the more advanced crossover bypass option too.

Erik

 

[tsv_1]

Erik,

Just keep in mind that when passively bi-amping you'll want to ensure level matching from your amplifiers. It's a non-issue if you plan to use the same model amps to drive HF and LF... But (there's always a but) if for example you're thinking maybe different amps (e.g. tubes on top and SS underneath as many folks have done with wonderful results) you may well have to deal with different gain factors between the two amps. If so, you would need to attenuate the line level signal into the higher-gain amp. There are attenuators out there for that very purpose, but I would ask... heck, if going that far, maybe it's worth looking at active cross-overs anyway.

Cheers

 

[slowGEEZR]

Erik, here's a link to one type of those attenuators Todd mentioned. It's called the B2- Biamp Buffer. http://www.firstwatt.com/b2.html

 

[tsv_1]

Erik, here's a link to one type of those attenuators Todd mentioned. It's called the B2- Biamp Buffer. http://www.firstwatt.com/b2.html

Thanks Steve... I hadn't seen Nelson's B2, and reading through it reminded me that if the pre-amp output is high-ish impedance (e.g. many tube pres), buffering the signal should even be considered when attempting to drive multiple identical amps.

 

[eknuds01]

Yeah the gains between the amps may be different. Spike has sent me some info on how to match the gains. Otherwise it's possible that panels could be louder than the woofer, or vice versa.